This research plan is multidisciplinary, cell and photobiological study of in vivo and in vitro melanogenesis in mammals, especially humans. In the in vitro studies, we shall use the method we have developed and successfully used over the past three years in maintaining normal human melanocytes in pure cell cultures. Melanocytes will be studied while isolated from the effects of other cell types, especially keratinocytes, a condition not found in vivo. Using radioactive labeling and autoradiography on the light and electron microscopic level, we will establish a timetable for the melanogenic processes of the cultured human melanocyte. Once established, the extracorporeal factor controlling melanogenesis, ultraviolet irradiation will be selectively applied to our cultured melanocyte system at various times in the cell lifespan. Establishing the action spectra and dose responses to U.V., the maximal effects on melanogenes is by this agent will be determined. Cultures of albino and black guinea pig epidermal melanocytes will also be used as a model system where melanizationis inhibited due to genetic mutation. Mixed cell cultures (melanocytes and keratinocytes) of guinea pig or human epidermis will be utilized to study the possible role of keratinocytes in the melanogenic process and in responses to stimulus by ultraviolet light. Noting the limitations of our culture systems, the tails of variously pigmented mice will also be used as an in vivo system to study the long-term effects of ultraviolet light and in combination with a photosensitizer, psoralen (PUVA), or a carcinogen (DMBA). This is of great clinical significance, as PUVA treatment is used for therapy of a variety of skin disorders, such as psoriasis, vitiligo, mycosis fungoides, and atopic eczema, while our study of the effect of the carcinogen DMBA and the phototoxic agent, UVB will contribute to understand the role of ultraviolet in the origin of melanomas and explain alterations in the melanogenic processes as are found in various pigmentary disorders such as albinism and vitiligo.